The present invention is related to transmission electron microscopes and methods of inspection using them, and in particular, to methods of inspection of semiconductor substrates.
A method of detecting crystal defects in specimen using conventional transmission electron microscopes has been disclosed, for example, in Transmission Electron Microscopy, Plenum Publishing Corporation (1996), p.379xcx9cp.445. In this method, the sample is tilted so that the electron beam satisfies the diffraction conditions for the crystal defect of the specimen, and a specific diffraction electron beam is made to pass through using objective lens aperture while all other electron beams are cut off, thereby detecting the crystal defect by increasing the contrast of the crystal defect.
In the above method of detecting crystal defects in specimen using conventional transmission electron microscopes, the transmission electron microscope image is observed while setting the specimen inclination in various directions, and the presence or absence of crystal defects is judged from the contrast of the image.
However, in the range in which the specimen stage can be adjusted mechanically, it is difficult to make the shift in the image when the specimen is inclined to smaller than about 1 xcexcm. As a result, in order to inspect the presence or absence of crystal defects at the same location, it was necessary to move the specimen stage manually so as to observe the same field of view whenever the specimen inclination is changed, and hence a long time was necessary until the crystal defect could be detected. Therefore, inspecting for the rate of occurrence of crystal defects over a wide field of view was almost impossible because of the extremely long time required for such an inspection. On the other hand, although it is possible to inspect for the rate of occurrence of crystal defects over a wide field of view by limiting the direction of electron beam incidence to only one direction, since the detection of crystal defects is strongly dependent upon the direction of incidence of the electron beam, as has been described above, it is possible that the crystal defects are not detected even if they are present, and hence it is not possible to inspect for the accurate rate of occurrence of crystal defects. In addition, after inspecting for the rate of occurrence of crystal defects over a wide field of view, if it is necessary to observe in detail a specific defect location part, it is necessary to move the specimen stage thereby bringing the position of that defect to within the field of view for analysis.
However, all stage movements are done manually, and since the operator has to calculate the address positions of the defect locations, it becomes necessary to start moving the stage from the origin of counting the position each time while counting the address, it takes a considerably long time to move to the location where each defect was detected, and also, there is the problem that the stage cannot be moved to the correct location of the defect because of manual errors in counting the address.
For example, consider that there are 256xc3x97256 memory cells in one memory mat, these are subjected to the presence or absence of defects with the direction of electron beam irradiation being limited to one direction. It takes 30 seconds to inspect the memory cells in units of 16 cells and to verify the presence or absence of defects in each image, which is the total time including time required to move the stage manually, to adjust the focus, and to judge the presence or absence of defects by manual observation. Under these conditions, in order to complete the inspection, it takes a very long time of 1.4 days (=(256xc3x97256)/(16xc3x970.5)=2048 minutes). Because of this, this inspection method is not practical since even the defect detection rate is low and a very long time is required for inspection.
A method of inspection using a conventional electron microscope apparatus has been disclosed, for example, in Japanese Unexamined Patent Publication No. Hei 10-74813. In this method, the sample is irradiated with an electron beam, and the image is obtained from the intensity of the secondary electrons generated from the surface of the specimen, and the judgment of defects is made from the contrast of the image. Further, as has been disclosed in Japanese Unexamined Patent Publication No. Hei 5-215694, as a method other than electron microscopes, the specimen is irradiated with X-rays, a transmission image of the specimen pattern is obtained and the judgment of defects is made from that pattern.
In the above inspection methods using an electron microscope apparatus, since the sample is irradiated with an electron beam and the image is obtained from the intensity of the secondary electrons generated from the surface of the specimen, although it is possible to judge the shape defects on the surface of the specimen, it is not at all possible to evaluate the crystal defects in the specimen. In addition, when the pattern of the specimen is observed by irradiating the specimen with X-rays, only the shape of the specimen can be observed, and the crystal defects in the specimen cannot be evaluated.
In the conventional method of inspecting crystal defects in the specimen using a transmission electron microscope apparatus, since the crystal surface satisfying the black conditions appears as a contrast in the transmission electron microscope image, it is not possible to judge that there are no defects by merely observing from one direction. Therefore, it is necessary to set the specimen inclination at various angles and to judge the presence or absence of crystal defects from the image contrast, it takes a very long time to judge the presence or absence of crystal defects in one section to be inspected, and an extremely long time is required to inspect for the crystal defect occurrence rate in a wide field of view. In addition, in a wide field of view, the defect detection rate decreases if the inspection for determining the crystal defect occurrence rate is done by limiting the direction of electron beam incidence to only one direction. In addition, after inspecting, during observation and analysis in detail of a specific defect location part, it is necessary for the operator to move manually the specimen stage to the address location of the part with the defect, and hence a long time is required to move the stage to the defect detection part, and also there is the possibility of not being able to move to the defect detection part because of human errors in counting the address. Further, in the method in which the image is obtained from the secondary electrons emitted from the specimen surface and the Good or No Good judgment is made from the contrast of that image, although it is possible to judge the shape defects on the surface of the specimen, it is not at all possible to evaluate the crystal defects in the specimen. In addition, even in the method of observing the pattern of the specimen when it is irradiated with X-rays, it is only possible to observe the shape of the specimen. The purpose of the present invention is to provide a transmission electron microscope apparatus and a method of inspection using such an apparatus, in which it is possible to detect automatically the crystal defects and shape abnormalities in the specimen over a wide area of the specimen at both a high speed and a high probability rate, and also possible, during detailed analysis after inspection, to set automatically the parts where crystal defects or shape abnormalities were detected to the analysis position.
In particular, the present invention is intended to provide a method and apparatus for identifying crystal defects in the base material caused by preparation using a base material having a crystalline structure.
For example, if we consider that there are 256xc3x97256 memory cells in one memory mat, and it takes 0.5 seconds to judge the presence or absence of defects by inspecting the memory cells in units of 16 cells, it takes 34 minutes to complete the inspection (that is, (256xc3x97256)/(16xc3x970.5)=2048 seconds=34 minutes), and hence this becomes a very practical inspection method.
In order to achieve the above objectives, the configuration of irradiating the specimen with an electron beam automatically from several directions is described below.
In the present invention, in a transmission electron microscope provided with an electrostatic lens with one or more stages for making the electron beam generated from the cathode a beam with high energy, a condenser lens and objective lens with one or more stages for irradiating the electron beam on the specimen in a direction parallel to the optical axis of the transmission electron microscope, a specimen holder for supporting the specimen located at the objective lens or below it, one or more stages of imaging lens for enlarging the acquired image, an image acquisition apparatus for detecting and recording the acquired image, and one or more stages of a deflection coil for varying the angle of incidence of the electron beam on the specimen, it has been made possible to obtain the detection rate of crystal defects at a high efficiency by putting emphasis on the contrast in the transmitted beam and from the contrast difference at the same location on the specimen at a plural number of incident angles using said deflection coil to vary the electron beam incidence angle over a number of different values.
Furthermore, a computer program or an electronic circuit is provided for driving in a linked manner the one or more stages of the image shift coils that move in two dimensions the imaging plane of the objective lens, said deflection coil, and said image shift coil, and it has been made possible to detect the crystal defects at high speeds by compensating the image shift due to electron beam irradiation at various angles of incidence in said image acquisition apparatus because of driving in a linked manner said deflection coil and said image shift coil.
In addition, it has been made possible to automatically detect at high speeds the crystal defects and shape abnormalities over a wide area of the specimen by making the movement of the specimen stage automatic, and also, the configuration has been made so that the addresses of the parts with crystal defects or shape abnormalities are recorded, and by reading them out at the time of detailed analysis after inspection, it becomes possible to set automatically the part with crystal defects or shape abnormalities at the analysis point.
In this manner, the present invention provides concrete apparatuses and methods that permit detection at speeds that are about 70 times faster than the conventional methods.
In other words, the present invention is one that was invented with the task of testing one sample (a DRAM of about 130,000 bits) in a time duration of about 30 minutes.
In a transmission electron microscope in which the electron beam generated from an electron source is accelerated to a specific voltage by an electrostatic lens, the accelerated electron beam is irradiated parallel to the optical axis on the specimen by a condenser lens and an objective lens, the angle of incidence of the electron beam on the specimen is varied by a deflection coil, the transmitted image of the specimen is magnified by a projection lens, and the intensity of the image is detected by an image acquisition apparatus, the present invention provides a transmission electron microscope apparatus with a configuration containing a controlling means by which the electron beam is irradiated from different incident angles on the same address-specified location of the specimen using said deflection coil, and a means for displaying on the display screen multiple transmission images obtained by impinging the electron beam at different angles of incidence.
In addition, in a transmission electron microscope in which the electron beam generated by an electron source is accelerated up to a specific voltage by an electrostatic lens, the accelerated electron beam is irradiated on the specimen in a direction parallel to the optical axis of the electron beam microscope by a condenser lens and an objective lens, the angle of incidence of the electron beam on the specimen is varied by a deflection coil, the transmission image of the specimen is enlarged by a projection lens, and the image intensity is detected by an image acquisition apparatus, the present invention provides a transmission electron microscope apparatus with a configuration containing a controlling means so that the electron beam is irradiated from different incident angles on the same location of the specimen using said deflection coil, a means for comparing the images obtained by impinging the electron beam at different angles of incidence with a reference image that is either a transmission image obtained by irradiating said electron beam on the specimen or an image formed based on the design values and recorded beforehand as the reference image, and a means for recording the presence of specimen defect according to the result of such comparison.
In addition, in a transmission electron microscope in which the electron beam generated from an electron source is accelerated to a specific voltage by an electrostatic lens, the accelerated electron beam is irradiated parallel to the optical axis on the specimen by a condenser lens and an objective lens, the angle of incidence of the electron beam on the specimen is varied by a deflection coil, the transmitted image of the specimen is magnified by a projection lens, and the intensity of the image is detected by an image acquisition apparatus, the present invention provides a transmission electron microscope apparatus with a configuration containing a means by which the electron beam is irradiated from different incident angles on the same location of the specimen using said deflection coil, the acquired multiple transmission images are compared with a reference image, and the presence of defects in the specimen based on the result of such comparison is recorded, a means for deflecting the electron beam using an image shift coil that compensates the shift in said transmission image due to changes in the angles of incidence of the electron beam, and a means for driving the deflection coil and the image shift coil so that the deflection of the electron beam by said deflection coil and the deflection of the electron beam by said image shift coil are linked with each other.
Further, the present invention provides a transmission electron microscope apparatus in which said reference image can be recorded beforehand as a basic image for said comparison.
The present invention provides a transmission electron microscope apparatus in which said reference image is a part of the images among the multiple transmission images obtained by impinging the electron beam from different angles of incidence.
The present invention provides a transmission electron microscope apparatus containing a means for recording the image at a specific position and its position address as determined by the judgment of the presence or absence of defects, and a means for displaying the image recorded in the specimen stage using that position address.
The present invention provides a transmission electron microscope apparatus containing a means for recording the image at a specific position and its observation conditions as determined by the judgment of the presence or absence of defects, and a means for displaying the image recorded in the specimen stage using those observation conditions.
In a method of inspection using a transmission electron microscope in which the electron beam generated by a cathode is accelerated up to a specific voltage by an electrostatic lens, the accelerated electron beam is irradiated on the specimen in a direction parallel to the optical axis of the electron beam microscope by a condenser lens and an objective lens, the angle of incidence of the electron beam on the specimen is varied by a deflection coil, the transmission image of the specimen is enlarged by a projection lens, and the image intensity is detected by an image acquisition apparatus, the present invention provides a method of inspection using a transmission electron microscope apparatus with a configuration including the method of irradiating the electron beam from different incident angles on the same location of the specimen using said deflection coil, comparing with a reference image the images obtained by impinging the electron beam at different angles of incidence, and recording the presence of specimen defect according to the result of such comparison.
In a method of inspection using a transmission electron microscope in which the electron beam generated by a cathode is accelerated up to a specific voltage by an electrostatic lens, the accelerated electron beam is irradiated on the specimen in a direction parallel to the optical axis of the electron beam microscope by a condenser lens and an objective lens, the angle of incidence of the electron beam on the specimen is varied by a deflection coil, the transmission image of the specimen is enlarged by a projection lens, and the image intensity is detected by an image acquisition apparatus, the present invention provides a method of inspection using a transmission electron microscope apparatus with a configuration including the method of irradiating the electron beam from different incident angles on the same location of the specimen, and the presence or absence of defects in the image is judged during the blanking period after each image of the multiple numbers of transmission images.
In addition, the present invention provides a method of inspection using a transmission electron microscope apparatus in which the angle of incidence of the electron beam is varied during the blanking period after acquiring each image.
In addition, the present invention provides a method of inspection using a transmission electron microscope apparatus in which the image is displayed after moving the specimen stage during the blanking period after acquiring each image.